9:00 AM - MQ03.01.03
Experimental Verification of Magnetic-Field-Induced Topological Phase Transition in Fe-Doped Topological Insulator (Bi,Sb)2Se3 Thin Films
Junichi Shiogai1,Yosuke Satake1,Grzegorz Mazur2,Shojiro Kimura1,Satoshi Awaji1,Kohei Fujiwara1,Tsutomu Nojima1,Kentaro Nomura1,Seigo Souma3,4,Takafumi Sato3,4,5,Tomasz Dietl2,4,Atsushi Tsukazaki1,3
Institute for Materials Research, Tohoku University1,International Research Centre MagTop, Institute of Physics, Polish Academy of Sciences2,Center for Spintronics Research Network (CSRN), Tohoku University3,WPI-Advanced Institute for Materials Research, Tohoku University4,Department of Physics, Tohoku University5
Thin film synthesis of the emergent quantum materials is a prerequisite technique to observe novel topological phases such as quantum Hall  or quantum anomalous Hall (QAH) state [2-5] and exotic proximity effects at hetero-junction with magnets and superconductors . The QAH phase accompanying a dissipation-less chiral edge channel has been achieved in one example of three-dimensional topological insulator (3D-TI), (Bi,Sb)2Te3 with a magnetic dopant Cr or V, which fulfills two requirements: (i) inducing an exchange gap by magnetic impurity doping and (ii) tuning Fermi level (EF) into the gap by electrostatic gating in a thin film form . A representative 3D-TI Bi2Se3 is another candidate platform to study such an exotic topological phase because of an inherently large bulk insulating gap . However, by comparing with a well-investigated (Bi,Sb)2Te3 3D-TI compound, there has been little progress on EF tuning technique in (Bi1-xSbx)2Se3 probably owing to a low solubility limit of Sb below x ~ 0.5 , making it difficult to study the Dirac feature of this system by electrical transport measurements. To date, we have developed a buffer layer technique to stabilize rich Sb-doped (Bi1-xSbx)2Se3 in molecular beam epitaxy. With precise tuning of Bi/Sb composition ratio and thickness in a field-effect transistor (FET), we materialized the EF tuning across the charge neutral point (CNP) [9,10].
In this study, based on these established EF tuning techniques, we investigate magneto-transport properties of Fe-doped (Bi1-xSbx)2Se3 heterostructures. The Fe-doped sample with EF tuned around CNP behaves like an insulator at zero magnetic field. By sweeping a perpendicular magnetic field, topological phase transition emerges from Anderson insulator to QAH state . A clear insulator-to-metal transition was observed in magnetoresistance with a large Hall resistance by application of a high magnetic field up to 24 T. Furthermore, a (Bi1-xSbx)2Se3-based FET exhibits the large Hall resistance approaching the quantized value (h/e2) at around 14 T. With these set of the data, we concluded that a magnetic-field-induced QAH state was verified in Fe-doped (Bi1-xSbx)2Se3 thin films. Combining well-regulated growth technique for precise tuning of EF and high-field transport measurements sheds light on the hidden topological phases in a wide variety of emerging quantum materials.
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